hob: correctly set the selected image when loading a recipe

When the user saves their recipe based on an existing image type, loads it
in a newly run hob instance and clicks bake they should not be asked about
building packages vs an empty image up.

Partially addresses [YOCTO #1468]

(Bitbake rev: f4be83aae77a713e2b5a2d094651639b6e641031)

Signed-off-by: Joshua Lock <josh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/ui/hob.py

@@ -144,6 +144,7 @@ class MainWindow (gtk.Window):
         self.build_succeeded = False
 
     def image_changed_string_cb(self, model, new_image):
+        self.selected_image = new_image
         # disconnect the image combo's signal handler
         if self.image_combo_id:
             self.image_combo.disconnect(self.image_combo_id)